This invention relates to a communication device for communication with a data carrier which is situated within a communication range of the communication device and which is movable through the communication range along a predetermined path, which communication device includes receiving means which are adapted to receive a data carrier signal which is supplied by a data carrier and which can be received with amplitude values of different magnitudes depending on the passage of the data carrier through the communication range.
A communication device of the type defined in the opening paragraph is known from U.S. Pat. No. 5,621,411 A.
During a process of determining the exact position of a data carrier relative to a communication coil configuration of a communication device, which data carrier is movable along a path, the known communication device utilizes means for computing the distance between the data carrier and the communication device, with the aid of which means the distance can be computed on the basis of an analog field strength of a data carrier signal received from the communication device. However, the know data carrier has the problem that the exact position of the data carrier with respect to the communication coil configuration can be determined only on condition that the data carrier has a given and consequently known orientation with respect to the communication coil configuration of the communication device. However, when the communication device is used in order to determine the exact position of a data carrier attached to, for example, a piece of cargo this condition can never be satisfied because the data carrier which is moved along a path by means of, for example, a conveyor arrangement may have an arbitrary orientation with respect to the communication coil configuration of the communication device. Furthermore, the known communication device has the problem that for determining the exact position of the data carrier the absolute value of the analog field strength is used, which particularly in view of tolerances in the fabrication of communication coils of different data carriers or tolerances in the fabrication or in operation of electric circuits of different data carriers may lead to invalidated results in the determination of the exact position. The invalidation of the results becomes particularly unacceptable when the absolute value of the analog field strength near a zero crossing of the analog field strength is used in order to determine the exact position because the means for computing the distance between the data carrier and the communication coil configuration can be utilized only when the field strength values are large enough, which reveals a fundamental problem of the known communication device, because the analog field strength of a data carrier signal received by the communication device usually exhibits small field strength values.
It is an object of the invention to solve the aforementioned problems of a communication device of the type defined in the opening paragraph and to provide an improved communication device such that, even for data carriers having arbitrary orientations with respect to a communication coil configuration of the communication device, a reliable determination of the exact position of the data carrier with respect to the communication coil configuration is guaranteed and tolerances of the data carrier do not lead to invalid results in the determination of the exact position.
The aforementioned object is achieved with a communication device of the type defined in the opening paragraph in that detection means for detecting a value representative of the maximum amplitude value of the data carrier signal supplied by a data carrier and received by the receiving means have been provided, and the detection means are adapted to generate and supply a detection signal upon detection of the value representative of the maximum amplitude value.
As a result of the provision of the characteristic features in accordance with the invention it is advantageously achieved that the exact position of the data carrier which is moved along a given path, for example with a constant speed by means of a conveyor arrangement, can be determined through the detection of the value representative of the maximum amplitude value after the generation and supply of the detection signal, in the first place for a data carrier that is oriented arbitrarily relative to the communication coil configuration, in the second place independently of its tolerances, and in the third place independently of the materials in its vicinity. Moreover, the advantage is obtained that, even in the case that two or more adjacent data carriers which are moved through the communication range with the aid of the conveyor arrangement at substantially the same time, a sequence of these data carriers can be determined with a high accuracy merely with the aid of the detection signals produced by the data carrier signals of each data carrier.
As a result of the provision of the characteristic features as defined in claim 2 it is advantageously achieved that the detection of value of the received data carrier signal which is representative of the maximum amplitude value can be detected with the aid of the control means and the memory means and the comparison means without knowledge of an absolute value of an amplitude value of the data carrier signal and advantageously by means of a comparison of amplitude values of the received data carrier signal which have been determined in temporal succession. During the comparison it is very simple to determine a change in course of a gradient of the amplitude values of the received data carrier signal determined in temporal succession, as a result of which in the case of a zero crossing in the course of the gradient the comparison means can determine this zero crossing with the aid of the comparison result signal and the detection signal can be generated in conformity with the comparison result signal.
As a result of the provision of the characteristic features as defined in claim 3 it is advantageously achieved that during the formation of the detection signal the comparison result signal enables not only the value representative of the maximum amplitude value to be determined but also enables a movement of the data carrier relative to the communication coil configuration to be detected because during a movement of the data carrier comparison result signals generated in temporal sequence, which represent for example differences between temporally adjacent amplitude values, should differ at least slightly from one another.
As a result of the provision of the characteristic features as defined in claim 4 it is advantageously achieved that the detection signal generator can be started with the aid of the comparison result signal and that subsequently, with the aid of the detection signal generator characteristic-value signals, which occur in the communication device and which may, for example, be formed by data contained in the data carrier signal, can be used for the generation of the detection signal, which data can then be supplied to a control device, which can be connected to for example the communication device, for further processing, essentially in synchronism with the detection of the value representative of the maximum amplitude value by the communication device with the aid of the detection signal.
As a result of the provision of the characteristic features as defined in claim 5 it is advantageously achieved that, as long as the data carrier is moved along its predetermined path, the time data enable the exact position of the data carrier to be determined precisely at any instant after the detection of the value representative of the maximum amplitude value.
The aforementioned aspects as well as further aspects of the invention will be apparent from the examples of embodiments described hereinafter and will be elucidated with the aid of these examples.
The invention will be described in more detail hereinafter with reference to two embodiments which are shown in the drawings by way of example but to which the invention is not limited.